1. Field of the Invention
The invention relates to accelerometers, and more particularly, to a process for fabricating a capacitance type tri-axial accelerometer used in micro electro-mechanical systems (MEMS).
2. Description of the Related Art
Known in the art is a method of fabricating an accelerometer capable of detecting acceleration along three orthogonal axes as disclosed in U.S. Pat. No. 7,361,523. This method, as shown in its FIGS. 15 and 16, forms two in-plane accelerometers (the first and second accelerometers) positioned at right angles to each other so as to assess acceleration in two directions within the plane thereof, and a third accelerometer disposed out-of-plane to measure acceleration in a direction perpendicular to the plane where the first and second accelerometers are positioned.
Such a three-axis accelerometer made by the method mentioned above has several disadvantages. The first is that the location of the third accelerometer is different from that of the first and second accelerometers so that the size of the three-axis accelerometer as a whole is too large to be suitable for micro electro-mechanical systems. The second disadvantage is that the comb-like capacitive plates of the three-axis accelerometer are combined in a mechanical way such that the assess value of each of the accelerometers unavoidably affect each other. The result is that the measurement taken by the three-axis accelerometer is inaccurate. Furthermore, each set of the comb-like capacitive plates of the three-axis accelerometer is used not only as capacitive elements but also as a proof mass, thereby limiting the mass that can detect external accelerations and reducing sensitivity.
It is therefore a principal object of the present invention to provide a process for fabricating a capacitance type tri-axial accelerometer having a suitable size for use in micro electro-mechanical systems.
Another object of the present invention is to provide a process for fabricating a capacitance type tri-axial accelerometer having a higher sensitivity than prior art.
A further object of the present invention is to provide a process for fabricating a capacitance type tri-axial accelerometer which can precisely sense external accelerations.